Intoxicated drivers are a major cause of traffic accident fatalities in the United States. A recent NHTSA report showed that 40% of the total accident fatalities in the U.S. in the year 2003 were alcohol related. More specifically, 12,373 motor vehicle occupants were killed in crashes that involved a blood alcohol concentration (BAC) of 0.08 g/dL or higher. This equates to over 33% of the 37,132 U.S. motor vehicle fatalities in 2003. In addition to the societal impact, the cost of such crashes in the U.S. is about $40 billion per year. It is well established that the rate of fatal traffic accidents per mile traveled is related to a driver's BAC and that there is a correlation between impairment in driving skills and the driver's BAC. The definition of drunk driving in the U.S. involves a BAC level of either 0.08 g/dL or 0.10 g/dL, depending on the particular state law. Moreover, the states of the U.S. that currently have a 0.10 g/dL BAC limit have passed laws lowering the BAC limit to 0.08 g/dL, to take effect soon. A primary countermeasure to combat drunk driving in the U.S. is the criminal justice system, which employs deterrents and sanctions against drunk drivers. Various other approaches to combat drunk driving have been utilized.
One existing approach to combat drunk driving utilizes an electrochemical sensor that measures ethanol concentration in air. Ethanol concentration in human breath is a good indication of BAC. Inside the air sacs in the human lung, there is a chemical equilibrium between the concentration of ethanol in the air and the concentration of ethanol in an individual's blood. For law enforcement purposes, an electrochemical sensor is built into an object such as a clipboard or flashlight that a police officer can, under certain circumstances, justifiably insert into a vehicle. However, currently available electrochemical sensors have a limited lifetime and typically must be replaced after about three years. To be used as an on-board component of the safety system, an ethanol sensor must have a lifetime of at least ten to fifteen years. Another electrochemical sensor that is used includes a device that is pressed against an individual's skin to determine alcohol intoxication through remote detection of ethanol that evaporates from the driver's skin. Other approaches involve passing infrared through the driver's extremities, such as a finger, or using Raman spectroscopy to measure the concentration of ethanol in the fluid at the surface of the driver's eyes. These approaches are impractical for on-board vehicle use as well.
Another approach to combat drunk driving uses a heated film of metal oxide that changes electrical resistance in response to ethanol concentration. Such sensors are used in commercially available “breath interlocks,” sometimes mandated following a drunk driving conviction, which require the driver to breathe into a tube to check for excess breath alcohol before a vehicle will start. However, such sensors do not have sufficient sensitivity for passive detection of a drunk driver in regard to measuring ethanol vapor in the air of a vehicle cabin. The breath sample blown into a tube is undiluted and so the detection level needed is only about 210 parts per million (ppm) of ethanol, by volume. A passive detection system needs to be about 1000 times more sensitive. Also, the minimum ethanol concentration that can be reliably detected with a metal oxide film is typically in the range of 10 to 50 ppm. A further disadvantage is that the response to ethanol concentration is non-linear as a function of ethanol concentration.
Infrared detection has also been used to quantify ethanol concentration in breath for law enforcement purposes, but the instruments used typically have a path length of about 1 meter making them large and bulky. To achieve the increased sensitivity to ethanol needed for passive sensing in a vehicle cabin, utilizing this instrument type, the path length could be increased. However, to use infrared detection and achieve the required sensitivity for passive detection would require a path length on the order of 100 meters. This is impractical for an on-board sensor.
U.S. patent application Ser. No. 20040141171, assigned to Delphi Technologies, Inc., filed Jan. 21, 2003, provides increased chemical sensitivity to ethanol by using a vapor concentrator. Ethanol vapor is collected by passing air containing ethanol over an adsorber and the adsorber is subsequently heated to release the ethanol vapor. Chemical sensors are then utilized that detect ethanol vapor by measuring its effect on the electrical conductance of a heated metal oxide film on a ceramic substrate.
U.S. patent application, U.S. Ser. No. 11/033,677, filed Jan. 12, 2005, assigned to Delphi Technologies, Inc., provides for passive detection of ethanol vapor utilizing a vapor concentrator and an infrared detector. A further U.S. patent application, U.S. Ser. No. 11/033,703, filed Jan. 12, 2005, assigned to Delphi Technologies, Inc., provides for passive and active detection of ethanol vapor utilizing a vapor concentrator and an infrared detector in addition to an active breathalyzer.
While these systems provide a measurement of ethanol vapor, environmental factors can affect vapor concentration (ethanol vapor and CO2) from a driver's breath before being picked up by a chemical sensor intake.